title: Acute physiological and performance responses to repeated sprints in varying degrees of hypoxia.
abstract: OBJECTIVE
  Our aim was to determine the effects of different inspired oxygen fractions on repeated sprint performance and cardiorespiratory and neuromuscular responses, to construct a hypoxic dose response.
  
  
  METHODS
  Nine male well-trained multi-sport athletes completed 10×6s all-out running sprints with 30s recovery in 5 conditions with different inspired oxygen fraction (FIO2: 12%, 13%, 14%, 15%, 21%).
  
  
  METHODS
  Peak running speed was measured in each sprint and electromyography data were recorded from m. vastus lateralis in parallel with heart rate and blood oxygen saturation. Cardiorespiratory response was assessed via breath by breath expired air analysis and muscle oxygenation status was evaluated via near infrared spectroscopy.
  
  
  RESULTS
  In parallel with the higher heart rate, minute ventilation, blood lactate concentration, and muscle deoxygenation; lower blood oxygen saturation, pulmonary oxygen uptake and integrated EMG (all p<0.05) were registered in all hypoxic conditions, with the greatest changes from baseline observed during the 13% trial. However, fatigue index and speed decrement were significantly greater only during the 12% vs 21% trial (p<0.05).
  
  
  CONCLUSIONS
  Physiological responses associated with performing 10×6s sprints interspersed with 30s passive recovery was incrementally greater as FIO2 decreased to 13%, yet fatigue development was significantly exacerbated relative to normoxia (FIO2: 21%) only at the 12% FIO2.
authors.affiliation: Sports and Health Sciences, Exeter University, United Kingdom. Electronic address: j.bowtell@exeter.ac.uk.
authors.forename: Joanna L
authors.initials: JL
authors.lastname: Bowtell
authors.affiliation: Lawn Tennis Association, United Kingdom.
authors.forename: Karl
authors.initials: K
authors.lastname: Cooke
authors.affiliation: Physical Education and Sports Sciences, Limerick University, Ireland.
authors.forename: Rachel
authors.initials: R
authors.lastname: Turner
authors.affiliation: Sports and Exercise Science, London South Bank University, United Kingdom.
authors.forename: Katya N
authors.initials: KN
authors.lastname: Mileva
authors.affiliation: Sports and Exercise Science, London South Bank University, United Kingdom.
authors.forename: D Paul
authors.initials: DP
authors.lastname: Sumners
mesh_terms: D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D004576:Electromyography; D005221:Fatigue / Q000503:physiopathology; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010100:Oxygen / Q000008:administration & dosage / Q000097:blood*; D010101:Oxygen Consumption; D012123:Pulmonary Ventilation; D052097:Quadriceps Muscle / Q000502:physiology; D012420:Running / Q000502:physiology*; D055815:Young Adult
chemical_list: D019344:Lactic Acid; D010100:Oxygen
keywords: Electromyography; Fatigue; Near infrared spectroscopy